Add List<T> to ArrayView<T> extension for NET9.0+

Ramstack.Structures.Tests/Collections/ArrayViewExtensionsTests.cs

@@ -0,0 +1,29 @@
+namespace Ramstack.Collections;
+
+[TestFixture]
+public class ArrayViewExtensionsTests
+{
+    #if NET9_0_OR_GREATER
+
+    [Test]
+    public void List_AsView_Empty()
+    {
+        var list = new List<string>();
+        var view = list.AsView();
+
+        Assert.That(view.Length, Is.EqualTo(list.Count));
+        Assert.That(view, Is.EquivalentTo(list));
+    }
+
+    [Test]
+    public void List_AsView()
+    {
+        var list = new List<string> { "apple", "banana", "cherry", "kiwi", "elderberry" };
+        var view = list.AsView();
+
+        Assert.That(view.Length, Is.EqualTo(list.Count));
+        Assert.That(view, Is.EquivalentTo(list));
+    }
+
+    #endif
+}

Ramstack.Structures.Tests/Ramstack.Structures.Tests.csproj

@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>net6.0;net7.0;net8.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;net7.0;net8.0;net9.0</TargetFrameworks>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
     <LangVersion>preview</LangVersion>

Ramstack.Structures/Collections/ArrayViewExtensions.cs

@@ -133,4 +133,52 @@ static int Impl(ReadOnlySpan<T> span, T value, IEqualityComparer<T>? comparer)
             return -1;
         }
     }
+
+    #if NET9_0_OR_GREATER
+
+    /// <summary>
+    /// Returns an <see cref="ArrayView{T}"/> over the specified list.
+    /// Items should not be added or removed from the <see cref="List{T}"/>
+    /// while the <see cref="ArrayView{T}"/> is in use.
+    /// </summary>
+    /// <typeparam name="T">The type of the elements in the list.</typeparam>
+    /// <param name="list">The list to get the data view over.</param>
+    /// <returns>
+    /// A <see cref="ArrayView{T}"/> instance over the specified list.
+    /// </returns>
+    public static ArrayView<T> AsView<T>(this List<T>? list)
+    {
+        if (list is not null)
+        {
+            var count = list.Count;
+            var array = ListAccessor<T>.GetBuffer(list);
+
+            return new ArrayView<T>(array, 0, Math.Min(count, array.Length));
+        }
+
+        return ArrayView<T>.Empty;
+    }
+
+    #region Inner type: ListAccessor<T>
+
+    /// <summary>
+    /// Provides low-level access to the internal array buffer of a <see cref="List{T}"/>.
+    /// </summary>
+    /// <typeparam name="T">The type of the elements in the list.</typeparam>
+    private static class ListAccessor<T>
+    {
+        /// <summary>
+        /// Retrieves a reference to the internal array buffer of the specified <see cref="List{T}"/>.
+        /// </summary>
+        /// <param name="list">The list whose internal buffer is to be accessed.</param>
+        /// <returns>
+        /// A reference to the internal array used by the list.
+        /// </returns>
+        [UnsafeAccessor(UnsafeAccessorKind.Field, Name = "_items")]
+        public static extern ref T[] GetBuffer(List<T> list);
+    }
+
+    #endregion
+
+    #endif
 }

Ramstack.Structures/Ramstack.Structures.csproj

@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>net6.0;net8.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;net8.0;net9.0</TargetFrameworks>
     <Description>Provides various data structures and utilities.
 
 Includes three primary types: